Oddo M., Laudicina V.A., Badalucco L., Verdeguer M., Conte P., Palazzolo E .(2015), Short-term response of soil microorganisms to essential oils with allelopathic potential.

Oddo Martina, 2, 3, Verdeguer Sancho Mercedes María, 5, 6

2015

Oddo M., Laudicina V.A., Badalucco L., Verdeguer M., Conte P., Palazzolo E .(2015), Short-term response of soil microorganisms to essential oils with allelopathic potential.

Weeds are currently managed in agriculture as well as in natural and recreational green areas. Synthetic herbicides are usually preferred to control weeds for their easy use, large number of weed species controlled and fast and long lasting effect. However, they could damage ecosystems and human health, and also select resistant weeds biotypes. As alternative to the traditional synthetic herbicides, natural herbicides, based on allelopathic substances (allelochemicals obtained from plants or microorganisms) are more respectful to the environment, having less persistence and different biochemical modes of action. The aim of this research was to investigate the effects of five essential oils (EOs) with allelochemical potential on soil microbial community structure and activity. The tested EOs have been extracted by hydrodistillation from leaves of Eucalyptus camaldulensis Dehnh. (EUC); Eriocephalus africanus L. (ERI); Thymus capitatus (L.) Hoffmanns. & Link (TCP); Citrus reticulata Blanco and Citrus limon (L.) Osbeck. The extracted EOs were emulsified and applied to soil at three concentrations: LOW (0.143 mL EO g-1 soil), MED (0.286 mL EO g-1 soil) and HIGH (0.571 mL EO g-1 soil). EOs-treated soils were incubated in controlled conditions and destructively sampled after 15, 30, 90 and 120 days. Soil samples were analysed to determine soil microbial biomass, community structure (phospholipid fatty acids) and activity (soil respiration). Microbial biomass, total and specific microbial respirations of EOs-treated soils did not show significant differences, compared to the control treatment. On the contrast, the G+/G- ratio and fungi showed significant differences between EO treatments and control. Specifically, regardless of concentration, the G+/G- ratio was increased by TCP, and at the highest concentration, fungi was decreased by EUC, LEM and ERI, while increased by TAN. Our results demonstrated that tested essential oils could be sustainable for weed management as they have a small effect on soil microorganisms. In fact, although soil microbial community structure was affected by EOs, total microbial biomass as well as the overall metabolic capacity of soil was not. However, further studies are needed to understand if the observed shift in microbial community structure could alter more specific soil processes such as nitrogen turnover.